There are window films that are opaque- blocking all light. For use in a vehicle, black minimizes noticeability. There is zero visibility, it’s like a solid wall. So it obviously cannot be used on the front windshield or front door windows. The legality of which windows and to what degree they can be obscured varies by vehicle type and by state.
https://www.amazon.com/dp/B00XHXU7P...olid=2YHSJKAX396WM&psc=1&ref_=lv_ov_lig_dp_it
If you can see through a tint on one side, folks on the other side can see through it also, though not necessarily equally. The side with the lowest amount of ambient light can see the other side more easily. I have one way privacy film on a residential sliding glass door. From the exterior during the day, it reflects the outside surroundings like a mirror; at night with the lights on, the interior is clearly visible just as if the windows were bare. Here’s a picture demonstrating the point:
One of my requirements was to have windows all around. It lessens my blind spots when driving and I like being able enjoy the scenery when parked. But there are times when I want privacy. I tried several types of window coverings (curtains, DIY reflectix, window film, WeatherTech Sunshade, and others) in a futile effort to avoid spending $1000+ on professionally made covers. Writing the check was painful, but it was money well spent.
1. They are insulated, helping moderate any necessary mechanical heating or cooling efforts.
2. There's no storage because they magnetically attach to the window frame.*
3. They can be rapidly deployed/unfolded, only a few seconds per window.
4. Almost no light leakage, allowing for total privacy at night with interior lights on.
5. It's invisible from the outside- in conjunction with the 20% OEM tint, the windows just look black, can’t see the covers.
* I do not use covers on the front windshield, driver or navigator windows. I use a curtain to partition off the cab area, because it looks less suspicious than covering the front windows.
I don’t know what kind of vehicle you have, but WeatherTech makes window covers for a wide range of vehicles. Not the highest quality, but very reasonable prices.
https://www.weathertech.com/sunshade/